1. The Field of the Invention
This invention relates to improved loudspeaker systems. In particular the invention relates to improved loudspeaker systems incorporating differential area passive radiators (DAPR) with more than two acoustic surface areas.
2. Prior Art
A group of prior art devices, relating to the invention, include Clarke U.S. Pat. No. 4,076,097, and Dusanek U.S. Pat. No. 4,301,332. These devices are well characterized in xe2x80x9cAugmented Passive-Radiator Loudspeaker Systems, Parts 1 and 2xe2x80x9d by Thomas L. Clarke, found in the June and July, 1981 issues of the Journal of the Audio Engineering Society.
Another device relating to the invention is found in Geddes PCT WO99/18755. The Geddes device is essentially a bandpass implementation of the Dusanek system. It is characterized in xe2x80x9cThe Acoustic Lever Loudspeaker Enclosurexe2x80x9d found in the January/February 1999 issues of the Journal of the Audio Engineering Society.
These prior art devices configure their active transducers such that one side surface area is coupled through a chamber to one of three diaphragm surface areas of an augmented passive radiator (APR), which is also coupled to the outside environment at a second diaphragm surface area of the APR. An augmented passive radiator is defined as a passive dual cone radiator that has one surface area coupled through the main enclosure volume to the active transducer, a second surface area coupled to the outside environment and a third surface area enclosed in a sealed auxiliary chamber. The Dusanek and Clarke active transducers radiate into free space and the Geddes system operates as a bandpass with the second side of the active transducer coupled to a third internal chamber. Even with this difference all three systems still use the closed architecture approach of exposing only one of the three acoustic surface areas of the augmented passive radiator to the external environment while sealing off the two remaining surface areas into isolated internal chambers or, alternatively, not controlling the output of at least one of the two remaining surface areas through a predetermined opening.
It is also a limitation of these systems that the active transducer has only one side of its cone interacting with the augmented passive radiator and/or they also isolate the output of one of the surface areas of their augmented passive radiators into a sealed chamber so that only one surface area can generate acoustic output. To state it differently, an augmented passive radiator (or the equivalent acoustic lever as per Geddes) is a closed architecture system with an isolated auxiliary chamber that closes off the output and coupling of one of the two smaller coupling areas of the augmented passive radiator. The prior art closed architecture approaches limit the low frequency output capability and/or require a larger enclosure than the present invention.
A further limitation of the Geddes disclosure is that it only discloses the use of an augmented passive radiator in a series bandpass configuration which can be less favorable particularly for low transformation ratio alignments.
The present invention provides an enhanced acoustic output through the use of an open architecture application of a differential area passive radiator (hereafter referred to as DAPR) having three substantially separate acoustic surface areas. A large or primary acoustic surface area, a smaller or unitary surface area, and a second smaller or differential surface area. The DAPR can be realized with the combination of two loudspeaker cones of different sizes attached back to back, each having their own surround/suspension. Alternatively the DAPR can be realized with one loudspeaker cone with a surround/suspension at the large end of the cone opening and another surround/suspension at the small end of the cone opening. The front and/or the rear of the DAPR is blocked off to acoustically isolate the areas. The DAPR enhances the output of an active transducer by operating as an acoustic transformer with a coupling ratio of the active transducer diaphragm area to the coupled acoustic surface area of the DAPR and the further ratio of one of the smaller acoustic surface areas of the DAPR to the largest surface area of the DAPR.
As disclosed in the parent case this invention advances the art of low frequency output with a three surface area differential area passive radiator in a novel configuration to eliminate the limitations of a closed architecture augmented passive radiator or acoustic lever by using an open architecture configuration of one or more differential area passive radiators.
It was shown that the open architecture is created by using a differential area passive radiator that has at least two of its three surface areas coupled to both sides of the active transducer and/or has a first and largest of the differential area passive radiator""s three surface areas output coupled into the listening environment either directly or indirectly through an opening of predetermined characteristics or passive acoustic radiator and a second of the differential area passive radiator""s three surface areas at least partially coupled into the listening indirectly through a passive acoustic radiator or opening of predetermined characteristics.
The differential area passive radiator can provide excellent acoustic performance when more than one of its acoustic surfaces has a predetermined, at least partially open, pathway to the external environment.
Further disclosed in the parent cases of this invention is the use of a parallel transfer of acoustic energy with the active transducer coupling acoustically in parallel with the differential area passive radiator by being coupled to the differential coupling area of the DAPR as an alternative to coupling in series through the small or unitary diaphragm surface area of the differential area passive radiator. This parallel coupling can offer favorable construction advantages for a given set of alignments, particularly those with a DAPR transformation ratio of less than two to one.